I agree with a lot of what has already been said. I've been waiting for a romance pack for a while. There's nothing like "Hot Date" or other themes from the past. Romance is either parceled in small amounts in different packs or ignored. I'd like a pack that really expands it
What interactions besides these above do you want? I'd want a lot of new romantic options. I agree that I'd want different romance styles so that sims are all a bit different and we aren't just watching the same few interactions over and over again. I think there needs to be a lot more romantic gestures whether sims are standing, sitting together, relaxing on a sofa or in bed or other places. Romance at home and romance in different venues could be a bit different from each other.
Imagine a chemistry system is introduced. How do you want it to operate? So, I'd like the ability to "set" romance if I have certain couples that I want to be immune from varying romantic interests or external attention. Other sims could have fluctuating chemistry, the sentiments are a step in this direction. I'd like the ability for sims to experience chemistry through doing things together or chemistry that just strikes at random. "I was out in the park and saw you and I just knew." Some sims could have attractions based on certain interests or features that they find attractive but there could be an ability to override that or to be surprised. I kind of like the idea of hidden attraction that gets discovered like someone else mentioned. Some sims could have a type and look for that. "Sporty sims; Geeky sims; great cook, etc".
Let's say a new world is added. What do you want it to be themed from? I'd like an Italian world but romance is so universal that it could be set anywhere or offer different new dating locations.
What new activities should be brought it? More dancing obviously, activities for dates - maybe with a random dating assignment for those who are set up. Cooking lessons. Activities at the bars. Speed dating, maybe, or group dates. Singles' events.
What should be added to build and buy mode? Attractive clothes and some frumpy sweats for those wanting to chill at home.
What should be added to CAS? Some new hairstyles but romance is a pretty universal theme.
What kind of aspirations or new whims should come with it? I agree that there should be dating or romance styles that vary. There should also be an option to lock a couple so that they don't experience random flirting outside the relationship if they aren't available or interested. We have two aspirations already but I think there could be romantic styles and new gameplay centered around themes like "Lucky in love", "Heartbreaker", "Just my type", or "Ready/Not Ready for Commitment". There could be goals to fall in love a certain way such as a sim who wants to meet others through a dating app or a sim who is against dating apps - not romantic enough or I just want to meet through friends. There could also be ways to set up different sims such as parents/siblings arranging a date or friends setting up a couple. There could be drama for exes. "Still an old flame" or an ex who won't let go.